When a pneumatic nail gun is used, the exhaust hood must be properly adjusted to prohibit exhaust air from directly blowing at the operator or at the ground in causing dust to fly about. As illustrated in FIGS. 1, 2, and 3, the exhaust hood 2 is fastened to the exhaust port 11' of the pneumatic nail gun 1' by a locating cup 22' and a screw 21'. When installed, a special tool must be used so that the screw 21' can be loosened for permitting the exhaust hood 2' to be adjusted to the desired angle. Therefore, the adjustment of the exhaust hood 2' is not easy.